From a walkway along the river Boyne, on the bank opposite Slane's famous castle, a walker saw a flash of feathered colour in the evening light.

It was a regular preamble so he kept a weather eye open for blue and green and reddish orange in a shimmering shyness of a bird hard to spot and often motionless, perched under a bridge or on a branch above water.

This was a kingfisher and there was a nest-hole on the bank where a pair came and went from a deep tunnel catching tiny fish by plunging with powerful and lengthy bills.

There is no nest material within, only the skeletons of fish which are used as 'duckboards' by the birds. There were fledglings ultimately and another family was successfully reared, escaping the predations of foxes and mink. But a hard winter ahead could be difficult.

I too had a kingfisher flash, rus in urbe, walking to the cemetery at Mount Jerome. In the snarl of Dublin traffic, above my head over a brambled wall, a lightning image of almost luminous blue and green caught the corner of an eye. And why not a kingfisher? Who would believe it? Here, a small river, the Poddle, enters a tunnel beneath the streets and exits in the Liffey below Christchurch.

Where there is water there will be found water birds, especially if there is cover. There is a regular grey heron further back at Mount Argus where once I also saw an egret, startling white, looking about in some apprehension. Once cattle grazed here. There was a water mill. The remainder of this place, once part of a monastery, is now a building site. It had been a camping area for homeless wanderers.

The kingfishers of the Poddle may be elusive but may not be as rare as a species in the Pacific of which there had been just three reported sightings. There has been controversy over the male moustached kingfisher of Guadalcanal in the Solomon Islands, The Washington Post reported.

Chris Filardi of the American Museum of Natural History said of the species: "They are ghosts. They reveal themselves in a thrilling moment and then they are gone." He found one he had been seeking for 20 years, then, in the parlance of science, he 'collected' it. In other words, he killed it.

There has been uproar. "This 'collecting' is a lame attempt to sanitise a totally unnecessary killing," said Prof Marc Belcoff of the University of Chicago. It was not a case of trophy hunting but too much research and conservation biology is "far too bloody". He asked: "When will the killing stop?"

Filardi insists 'his' kingfisher was known to be "unremarkably uncommon" by the local inhabitants and 'collecting' it was standard practice for field biologists. "Killing one kingfisher might help save them all," he said. And "thousands of pairs" remained.

This may be so, but history is littered with the stuffed carcasses of animals that were once the last of their kind. The learned journal Science has suggested that DNA, photographs and recordings of rare creatures should supply sufficient information for scientific research.